This application claims priority to an application entitled xe2x80x9cApparatus and Method for Gated Transmission in CDMA Communication Systemxe2x80x9d filed in the Korean Industrial Property Office on Apr. 12, 1999 and assigned Ser. No. 99-13610, filed on May 26, 1999, as well as Korean Application Ser. No. 99-19080, filed on Jul. 7, 1999, Korean Application Ser. No. 99-27355, filed on Jul. 8, 1999, and Korea Application Ser. No. 99-27398, the contents of all of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates generally to a CDMA mobile communication system, and in particular, to an apparatus and method for gated transmission which does not require a separate resynchronization process by assigning dedicated channels.
2. Description of the Related Art
A conventional CDMA (Code Division Multiple Access) mobile communication system primarily provides a voice service. However, the future CDMA mobile communication system will support the IMT-2000 standard, which can provide high-speed data service as well as voice service. More specifically, the IMT-2000 standard can provide high-quality voice service, moving picture service, an Internet search service, etc.
In a mobile communication system, data communication is typically characterized by bursts of data transmissions alternating with long non-transmission periods. The bursts of data are referred to as xe2x80x9cpacketsxe2x80x9d or xe2x80x9cpackagesxe2x80x9d of data. In the future mobile communication system, traffic data is transmitted over a dedicated traffic channel for a data transmission duration, and the dedicated traffic channel is maintained for a predetermined time even when the base station and the mobile station have no traffic data to transmit. The mobile communication system, after finishing transmitting traffic data over the dedicated traffic channel, maintains the downlink and uplink channels between the base station and the mobile station for a predetermined time even though there is no traffic data to transmit. This is done in order to minimize the time delay due to sync. reacquisition when there is traffic data to transmit.
The invention will be described with reference to a UTRA (UMTS (Universal Mobile Telecommunications System) Terrestrial Radio Access) mobile communication system. Such a mobile communication system requires many states according to channel assignment circumstances and state information existence/nonexistence in order to provide a packet data service as well as a voice service. For example, a state transition diagram for a cell connected state, a user data active substate and a control-only substate are well defined in 3GPP RAN TS S2 series S2.03, 99. 04.
FIG. 1A shows state transition in the cell connected state of the mobile communication system. Referring to FIG. 1A, the cell connected state includes a paging channel (PCH) state, a random access channel (RACH)/downlink shared channel (DSCH) state, a RACH/forward link access channel (FACH) state, and a dedicated channel (DCH)DCH/DCH, DCH/DCH+DSCH, DCH/DSCH+DSCH Ctrl (Control Channel) state.
FIG. 1B shows a user data active substate and a control-only substate of the DCH/DCH, DCH/DCH+DSCH, DCH/DSCH+DSCH Ctrl state. It should be noted that the novel gated transmission device and method is applied when there is no traffic data for a predetermined time.
The existing CDMA mobile communication system, which mainly provides voice service, releases a channel after completion of data transmission and connects the channel again when there is further data to transmit. However, when providing packet data service as well as voice service, the conventional data transmission method has many delaying factors such as reconnection delay, thus making it difficult to provide high-quality service. Therefore, to provide packet data service as well as voice service, an improved data transmission method is required. For example, in many cases, data transmission is performed intermittently, such as for Internet access and file downloading. Therefore, there occurs a non-transmission period between transmissions of packet data. During this period, the conventional data transmission method releases or maintains the dedicated traffic (or data) channel. If the dedicated traffic channel is released, a long time is required in order to reconnect the channel, and, if the dedicated traffic channel is maintained, channel resources are wasted and reverse power is wasted. To solve such problems, a dedicated control channel is provided between the base station and the mobile station so that for the data transmission period, a control signal related to the dedicated traffic channel is exchanged and for the non-transmission period, the dedicated traffic channel is released and only the dedicated control channel is maintained. Such a state is referred to as the xe2x80x9ccontrol-only substatexe2x80x9d.
A downlink (or forward link) for transmitting signals from the base station to the mobile station includes the following physical channels. A description of the physical channels which depart from the scope of the invention will be avoided for simplicity. The physical channels involved in the invention include a dedicated physical control channel (hereinafter, referred to as DPCCH) in which pilot symbols are included for sync acquisition and channel estimation, and a dedicated physical data channel (hereinafter, referred to as DPDCH) for exchanging traffic data with a specific mobile station. The downlink DPDCH includes the traffic data, and the downlink DPCCH includes, at each slot (or power control group), transport format combination indicator (hereinafter, referred to as TFCI) which is information about the format of transmission data, transmit power control (hereinafter, referred to as TPC) information which is a power control command, and control information such as the pilot symbols for providing a reference phase so that a receiver (the base station or the mobile station) can compensate the phase. The DPDCH and the DPCCH are time multiplexed within one power control group in the downlink, and the DPDCH and the DPCCH are separated from each other by orthogonal codes in the uplink.
For reference, the invention will be described with reference to the case where the frame length is 10 msec and each frame includes 16 power control groups, i.e., each power control group has a length of 0.625 msec. Alternatively, the invention will also be described with reference to another case where the frame length is 10 msec and each frame includes 15 power control groups, i.e., each power control group has a length of 0.667 msec. It will be assumed herein that the power control group (0.625 msec or 0.667 msec) has the same time period as the slot (0.625 msec or 0.667 msec). The power control group (or slot) is comprised of pilot symbol, traffic data, transmission data-related information TFCI, and power control information TPC in the downlink. The values stated above are given by way of example only.
FIG. 2A shows a slot structure including the downlink DPDCH and DPCCH. In FIG. 2A, although the DPDCH is divided into traffic data 1 (DATA 1) and traffic data 2 (DATA 2), there is a case where the traffic data 1 does not exist and only the traffic data 2 exists according to the types of the traffic data. Table 1 below shows the symbols constituting the downlink DPDCH/DPCCH fields, wherein the number of TFCI, TPC and pilot bits in each slot can vary according to a data rate and a spreading factor.
Unlike the downlink DPDCH and DPCCH, uplink DPDCH and DPCCH for transmitting signals from the mobile station to the base station are separated by channel separation codes.
FIG. 2B shows a slot structure including the uplink DPDCH and DPCCH. In FIG. 2B, the number of TFCI, FBI, TPC and pilot bits can vary according to the service being provided (which changes the type of the traffic data), or because of transmit antenna diversity, or because of a handover circumstance. The FBI (FeedBack Information) is information that the mobile station requests about the antennas at the base station, when the base station uses the transmit diversity antennas. Tables 2 and 3 below show the symbols constituting the uplink DPDCH and DPCCH fields, respectively.
Tables 1 to 3 show an example where there exists one DPDCH which is a traffic channel, wherein SF denotes spreading factor. However, there may exist second, third and fourth DPDCHs according to the service types. Further, the downlink and uplink both may include several DPDCHs.
An exemplary hardware structure of the conventional mobile communication system (base station transmitter and mobile station transmitter) will be described below with reference to FIGS. 3A and 3B. Although the base station transmitter and mobile station transmitter will be described with reference to a case where there exist three DPDCHs, the number of DPDCHs is not limited.
FIG. 3A shows a structure of the conventional base station transmitter. Referring to FIG. 3A, multipliers 111, 121, 131 and 132 multiply a DPDCH signal and DPDCH1, DPDCH2 and DPDCH3 signals, which have undergone channel encoding and interleaving, by gain coefficients G1, G2, G3 and G4, respectively. The gain coefficients G1, G2, G3 and G4 may have different values according to circumstances such as the service option and the handover. A multiplexer (MUX) 112 time-multiplexes the DPCCH signal and the DPDCH1 signal into the slot structure of FIG. 2A. A first serial-to-parallel (S/P) converter 113 distributes the output of the multiplexer 112 to an I channel and a Q channel. Second and third S/P converters 133 and 134 S/P-convert the DPDCH2 and DPDCH3 signals and distribute them to the I channel and the Q channel, respectively. The S/P-converted I and Q channel signals are multiplied by channelization codes Cch1, Cch2 and Cch3 in multipliers 114, 122, 135, 136, 137 and 138, for spreading and channel separation. Orthogonal codes are used for the channelization codes.
The I and Q channel signals multiplied by the channelization codes in the multipliers 114, 122, 135, 136, 137 and 138 are summed by first and second summers 115 and 123, respectively. That is, the I channel signals are summed by the first summer 115, and the Q channel signals are summed by the second summer 123. The output of the second summer 123 is phase shifted by 90xc2x0 by a phase shifter 124. A summer 116 sums an output of the first summer 115 and an output of the phase shifter 124 to generate a complex signal I+jQ. A multiplier 117 scrambles the complex signal with a PN sequence Cscramb which is uniquely assigned to each base station, and a signal separator 118 separates the scrambled signal into a real part and an imaginary part and distributes them to the I channel and the Q channel. The I and Q channel outputs of the signal separator 118 are filtered by lowpass filters 119 and 125, respectively, to generate bandwidth-limited signals. The output signals of the filters 119 and 125 are multiplied by carriers cos {2xcfx80fct} and sin {2xcfx80fct} in multipliers 120 and 126, respectively, to frequency shift the signals to a radio frequency (RF) band. A summer 127 sums the frequency-shifted I and Q channel signals.
FIG. 3B shows a structure of the conventional mobile station transmitter. Referring to FIG. 3B, multipliers 211, 221, 223 and 225 multiply a DPCCH signal and DPDCH1, DPDCH2 and DPDCH3 signals, which have undergone channel encoding and interleaving, by channelization codes (orthogonal codes) Cch1, Cch2, Cch3 and Cch4, respectively, for spreading and channel separation. Orthogonal codes are used for the channelization codes. The output signals of the multipliers 211, 221, 223 and 225 are multiplied by gain coefficients G1, G2, G3 and G4 in multipliers 212, 222, 224 and 226, respectively. The gain coefficients G1, G2, G3 and G4 may have different values. The outputs of the multipliers 212 and 222 are summed by a first summer 213 and output as an I channel signal, and the outputs of the multipliers 224 and 226 are summed by a second summer 227 and output as a Q channel signal. The Q channel signal output from the second summer 227 is phase shifted by 90xc2x0 in a phase shifter 228.
A summer 214 sums the output of the first summer 213 and the output of the phase shifter 228 to generate a complex signal I+jQ. A multiplier 215 scrambles the complex signal with a PN sequence Cscramb which is uniquely assigned to each mobile station, and a signal separator 229 separates the scrambled signal into a real part and an imaginary part and distributes them to the I channel and the Q channel. The I and Q channel outputs of the signal separator 229 are filtered by lowpass filters 216 and 230, respectively, to generate bandwidth-limited signals. The output signals of the filters 216 and 230 are multiplied by carriers cos {2xcfx80fct} and sin {2xcfx80fct} in multipliers 217 and 231, respectively, to frequency shift the signals to a radio frequency (RF) band. A summer 218 sums the frequency-shifted I and Q channel signals.
A conventional transmission signal structure of the base station and the mobile station will be made below. FIG. 5A shows how to transmit the downlink DPCCH and the uplink DPCCH when transmission of the uplink DPDCH is discontinued. This state, occurring after there is no data to transmit for a predetermined time, is called the control-only substate. FIG. 5B shows how to transmit the downlink DPCCH and the uplink DPCCH when transmission of the downlink DPDCH is discontinued because there is no data to transmit. As illustrated in FIGS. 5A and 5B, the mobile station constantly transmits the uplink DPCCH signal in spite of no DPDCH data in order to avoid a synchronization (sync) reacquisition process between the base station and the mobile station. When there is no traffic data to transmit for a long time, the base station and the mobile station make a transition to an RRC (Radio Resource Control) connection release state (not shown in the FIGs.). In this state, transmission of the uplink DPCCH is discontinued, but the mobile station transmits pilot symbols and power control bits over the DPCCH until the transition is completed, thereby increasing interference in the uplink (or reverse link). The increase in interference of the uplink causes a decrease in the capacity of the uplink.
In the conventional method, although continuous transmission of the uplink DPCCH in the control-only substate is advantageous in that it is possible to avoid the sync reacquisition process in the base station, it increases the interference to the uplink and the consumption of the mobile station power, causing a decrease in the capacity of the uplink. Further, in the downlink, continuous transmission of the uplink power control bits causes an increase in interference of the downlink and a decrease in the capacity of the downlink. Therefore, it is necessary to minimize the time required for the sync reacquisition process in the base station, to minimize the interference due to transmission of the uplink DPCCH, and to minimize the interference and mobile station power consumption due to transmission of the uplink power control bits over the downlink.
It is, therefore, an object of the present invention to provide a communication device and method for minimizing the time required for a sync reacquisition process between base station and mobile station, for minimizing the interference and power consumption of mobile station due to transmission of a uplink DPCCH, and for minimizing the interference due to transmission of uplink power control bits over a downlink when there is no data to transmit on the DPDCH for predetermined time.
It is another object of the present invention to provide a device and method for gating a dedicated control channel (DPCCH) signal on a gated transmission unit basis in a mobile communication system, wherein the gated transmission unit is either identical to an actual slot unit or different from the actual slot unit.
It is further another object of the present invention to provide a device and method for locating a power control bit in the last slot of each frame to control the power of the first slot of the next frame in a mobile communication system.
To achieve the above and other objects, a base station (or mobile station) according to the present invention determines whether there is data to transmit to the mobile station (or base station) on DPDCH. When there is no data to transmit on the DPDCH, the base station (or mobile station) gates transmission of control information according to a predetermined time period pattern within one frame on a dedicated control channel. Here, xe2x80x9cgated transmissionxe2x80x9d refers to transmitting the control information included in the DPCCH only at a specific power control group (PCG)/slot (or PCGs/slots) according to a predetermined time pattern. Control information transmitted from the base station to the mobile station includes TFCI information about a format of transmission data, TPC information for power control, and a pilot symbol. Control information transmitted from the mobile station to the base station includes TFCI information about a format of transmission data, TPC information for power control, a pilot symbol, and FBI information for requesting information about a phase difference between two antennas when the base station uses transmit diversity antenna. In a downlink DPCCH, the TFCI, TPC and pilot symbol in a predetermined nth power control group (or one slot) can be discontinuously transmitted in a frame during gated transmission. Alternatively, the pilot symbol in a predetermined nth power control group (or slot) and TFCI and TPC in (n+1)th power control group can be discontinuously transmitted in a frame. In an uplink DPCCH, the TFCI, TPC, FBI and pilot symbol in a specific power control group (or slot) are discontinuously transmitted during gated transmission. If there is a short data to transmit on DPDCH during gated transmission mode, the power control bit can be transmitted in all slots during the transmission of the short data. Further, a gating pattern for the downlink control information and a gating pattern for the uplink control information have an offset so that gating should occur at different time points.